Viscometer



April 11, 1950' P, G. ExLlNE ET AL l 2,563,660

I vIscoMETER Filed oct. e, 1948 2 sheets-sheet 1 POWER SUPPLY INVENTORSn v PAUL G.IEXLIN (0 BY JQHNRMKLNS r4 ATTORNEY P. G. ExLlNE ET AL2,503,660

VISCOMETER 2 Sheets-Sheet 2 H" UABHMmv En: Il' L w April 11, 195o FiledOct. 6, 1948 Patented Apr. 11,

UNITED *y STAT as PATENT orrlcs 'vlscoME'rEa raul GgExune, Tulsa,oki-a., and John n. Allam, Pittsburgh, Pa., assignors to Gulf Research &

Development Company, Pittsburgh, Pa., a corporation of.' Delawareapplication october s, 194s, serial No. 52,984

I This invention relates to a device for studying `and measuring therheological properties of` plastic-substances, and more'particularly. toa viscometer for determining the ow characteristics of such materials asgreases, drilling muds,

` paints, gumabitumensand the like. v

The viscosities of most plastic materials will change when suchmaterials are subjected to working For example, it is vwell known thatputty, grease and bread dough become more pliable after they have-beenkneaded, or more `specifically after they have been worked for a' periodof time Many of these plastics become more rigid again if they arepermitted to stand after they have been worked Thischaracteristic ofchange in viscosity or consistency with Vtrolled periods of working.Consequently, common viscometers do not give an accurate picture of howa plastic material such as a grease may `act in vvarious applicationsthereof.

The viscosity of a. grease identifies havior as well as its behaviorwhen used inthe of such plastics,` due 'tothe above factors, isnecessary before an accurate prediction of the behavior of a grease canbe made in a particular application and under actual operating con-l itsflow bey 7' claims. (Cm3-'56) from which'the apparent and absoluteviscosities l character described which will furnish informationfromwhich the amount of work done and lthe rate of doing work on thematerial under observation may be calculated. Another objectaccomplished by our invention is the provision of a viscometer whichwill furnish information of the material under observation may becalculated. A still further object accomplished by our invention is theprovision of a viscometer which will permit continuous studies to bemade on an initial sample of material under a variety of testconditions. A still further object accomplished by our invention is the'provision of a viscometer which will permit the testing of materials athigh static pressures. Other objects appear hereinafter.

Our invention is exemplified by the accompanying drawings and thedescriptive matter relating thereto. Referring to the drawings Fig. 1.isan elevation view partly in section illustrating the principal elementsof our viscometer. Fig. 2 is a schematic diagram of a hydraulic engineand the elements relating thereto which may be used to operate theviscometer shown inA Fig. 1. Fig. 3 is the schematic diagram of anelectrical timing system which may be used to ditions. Accordingly,these factors should also `be considered when making up schedules ofspecifications for various greases. It is apparent that commonviscometers do n ot supply such information, rand further, do notpermitv the making of continuous studies of a grease at various rates.and degrees of work to which the grease may be subjected.

Accordingly, the primary object accomplished by our invention is theprovision of a viscometer which will furnish information concerning theflow characteristics of plastic materials after they v have'beensubjected to various degrees-and-rates of work. A further objectaccomplished by our time the stroke of thehydraulic engine piston shownin Fig. 2l and the viscometer piston shown in Fig. 1.

Referring to Fig. 1, the heart of the viscometer is .a capillary tube orrestriction tube I, through which the material under observation isalternately passed in different directions. The ends of capillary tube iare coupled by means of couplings 2 to connecting lines 3 which areadapted to receive pressure lines connecting as close as possible withthe ends of capillary tube i. These pressure lines 4 are in turnconnected to pressure registering means shown as pressure gauges 5 sothat the pressure differential across capillary tube I may be determinedat all times. However, other pressure determining means, such as adifferential pressure gauge connected across capillary tube l, mayadvantageously be used. The ends of connecting lines 3 oppositecapillary tube i are fitted into collars 6 mounted on T- joints 1. Theupper passages of T-joints i are provided with caps 8 and these caps aretapped to accommodate plugs- 9 so that the plugs may be removedandpressuring devices attached to permit studies to be made at high staticpressures when desired. Collars 6 are also tapped to accommodate plugsi0 which may be removed to introduce the material to be tested into theviscometer. The lower portions of joints l are joined to cylinderhousings II which are adapted to support a cylinder I2 therebetween.Cylinder I2 is provided with a reclprocable piston I3, the purpose ofwhich is to force the material under observation through capillary tubeI. It can be seen that a free passage exists from the capillary tube Ito both sides of piston I3, so that as piston I3 is reciprocated thematerial being tested will alternately be forced back and forth throughcapillary tube I. Piston I3 derives its motivation from the hydraulicengine shown in Fig. 2 and is connected thereto by means of piston rodI4 and connecting rod I5. The side of piston I3 opposite piston rod I4lis provided with another rod I6, which may be an extension of piston rodI4, to equalize the volumetric displacement on both sides of piston I3as it is reciprocated. Temperature control of the viscometer is providedby means of a constant temperature bath I1 contained in a housing I8surrounding all the viscometer elements containing the material underobservation. Heat for this thermobath is supplied through mainelectrical heater I9 which is controlled by a variable auto transformer20. To facilitate a finer degree of heat control, main heater I9 isadjusted to produce slightly less than the amount of heat lost from thesystem, and an auxiliary heater 2 I, controlled by a temperaturecontroller 22, is provided to supplement the heat requirements of thesystem. The temperature of the system may be observed by reading aconveniently placed thermometer 23 situated in a thermometer well 24depending from the top of housing i8. An electrically operated stirrer25 is provided to improve the temperature distribution within thethermobath I1.

As stated above, reciprocation of piston I3 is accomplished by means ofthe hydraulic engine shown in Fig. 2 which connects with piston I3through connecting rod I5 and piston rod I4. This hydraulic engine ischaracterized by a cylinder 26 and a piston 21 therein which isreciprocated by the application of hydraulic pressure to alternate sidesthereof. The. hydraulic pressure is supplied from a sump tank 28 andpump 29 and the flow of uid through the varioiis lines shown in Fig. 2is as indicated by the direction of the arrows. From pump 29 thehydraulic fluid is forced through a relief valve 3u and to apilot-operated four-way valve 3l which directs the fluid to alternatesides of piston 21. A flow control valve 32 is placed in the system tocoact with relief valve 3B and bypass pressure uid to sump tank 28 whenthe pressure and flow of uid become excessive and consequently conyposition of valve 3| is determined by a pilot valve 33 so that,depending upon the position of pilot valve 33, hydraulic fluid will beapplied either to the right or left of piston 21. The connecting rod I5or the piston rod upon which piston 2T is mounted is provided with anextension 34 which extends beyond the engine cylinder 26, and thisextension 34 will of course reciprocate with piston 21. Extension 34 isprovided With adjustable trigger means 35 which are adapted to cooperatewith pilot valve 33 at the end of each stroke of piston 21 to reversethe flow of fluid through pilot valve 33. This will of course reversethe flow of uid through pilotoperated valve 3i so that at the end ofeach lill stroke of piston 21 the flow of fluid to the piston willautomatically be reversed and the stroke of the piston will be reversedaccordingly.

To determine the rate of ow of the material under observation throughcapillary tube I means to time the stroke of piston I3 are provided.Thus, knowing the volumetric displacement of piston I3 and the time ofthe stroke, it is possible to compute the rate of flow through capillarytube I. Since the strokes of pistons I3 and 21 are equal and since shaftextension 34 is operatively connected to piston 21, the velocity ofextension 34 will be equivalent to the velocity of piston I3. Forinstance, to time the stroke of piston I3, a cam 36 is mounted onextension 34 so as to engage one of a pair of contacts 31 and 38 at thestart and nish of each stroke of the system. These contacts areintegrally connected with an electric timing system so that the time ofeach stroke may simply be read from a clock or recorder. An example ofsuch a timing system is shown in Fig. 3 wherein a clock 39 is providedto register the time of each stroke. This clock is operatedby a motor 40which is constantly running, having been connected across a source ofpower. An electrically operated magnetic clutch 4I is provided toproduce operative engagement of motor 40 with the clock mechanismwhenever clutch 4I becomes energized, or more specically, when both ofcontacts 31 and 38 are closed. Thus, in the positions of the elements asshown in Fig. 3, as cam 36 moves to the left, contact 38 will becomeclosed and clock 39 will begin to operate. However, upon reaching theend of its travel, cam 36 will open contact 31 causing thede-energization of clutch 4i so that the operation of clock 39 will bestopped. Upon the reverse stroke cam 36 will close contact 31, startingthe clock, and nally will open contact 38, stopping the clock at the endof the piston stroke. A condenser 42 may be connected across thecontacts to suppress arcing.

The operation of the viscometer simply consists in introducing thematerial to be tested into the system and starting pump 29 to operatethe hydraulic engine and reciprocate piston I3. Temperature controls maybe varied as desired and the speed of recprocation of piston I3 may alsobe varied at will by minor adjustments in the hydraulic system. Theremaining test procedure then consists in reading from pressure gauges 5the pressure differential across capillary tube I and observing the timeof each piston stroke.

It is then possible to compute from known information and thatinformation which is observed during testing operations the apparent andabsolute viscosities of the material within the viscometer. Polseuilleis credited with the mathematical development which led to an equationwhich would permit measuring Viscosity of a. Newtonian liquid by meansof capillary tubes. One form of this equation is as follows:

u=1rPr4= Pr/2L Shearing stress wherein asoaeoo r=Radius of capillarytube. L=Length of capillary tube. P=Pressure differential across thecapillary tube. Q=Flow rate. B1=Shearing stress at they capillary walls.

I'he equation for shearing stress at the capillary walls is as follows:

lrPy

wherein r, P and L are as designated hereinabove. Using the value of Robtained from Equation 2 and the value of S1 obtained from Equation 3,the absolute viscosity may be obtained merely by dividing the shearingstress by the rate of shear in accordance with Newtons fundamental den'-nition of viscosity:

The above viscosity information can be obtained at any time sincecontinuous studies of a sample are made possible by the use of ourviscometer. The material under test can be worked any amount beforeviscosity results are recorded. The material under test may then beworked even more and another group of viscosity results may be recorded.At the end of any working schedule, viscosity data may be recorded, arest period permitted, and another set of viscosity data may beobtained. These working schedules may include various rates at which thework had been done and both the rate of doing work and thevamount ofwork done may be determined and expressed in fundamental units. Theseresults are obtained from the flowpressure data as shown in thefollowing equations:

wherein P= Pressure diierential across the capillary tube.

-g-Flow rate through the capillary tube.

The flow rate may be obtained simply by dividing the volumetricdisplacement of piston I3, which is-.xed and easily obtainable, by thetime'required for each stroke. Total work done merely requires amultiplication of the work rate by the time involved:

Total work= W=(%7X t (6) n' the work rate changes, an 11: usually wm due#francaises wherein ing feature.

a j to. the thixotropic nature of thematerial under observation, thetotal work may be obtained by making a diagram of work rate yplotteqzi.as a.

function of .time and thenintegrating the area under the curve. f

Itis apparent that many modiilcations of `our inventionmay be made yandmany equivalents of the elements shown herein may be substituted withoutdeparting from the spirit of the invention. For example, this inventionis not to be limited to the particular type oi' engine disclosed hereinfor reciprocating piston i3, as many other engines known to the artwould be suitable. Furthermore, the means employed for the timing of lthe stroke of piston I3 is included herein merely to illustrate a methodwhich may; advantageously be used-and should not be considered as alimit- Other means for determining iiow rate may be used withoutdeparting from lour invention. For instance, a flow gauge may beinstalled in the system directly in the path of the material beingpassed through the capillary tube. In addition, theform of temperaturecontrol which has been illustrated may be variously.'

modified and changed, the important thing being that adequatetemperature control is constantly v maintained during operation of thekviscometer.

One of the most important advantages of our invention is that itprovides a viscometer which is capable of making viscositydeterminations of a thixotropic material after it has been worked for aperiod of time. Another advantage is that both the amount of work doneand the rate of doing work may be varied so that a more accurateindication of what the material under test may do under actualoperatingconditions can be obtained. This is partly due to the fact that scribedherein are intended to be merely illusfl trative of our invention and inno manner should they be considered as limitations thereof or aslimiting the scope of the appended claims hereinafter made. v

What we claim is:

1. A device for determining the ilow characteristics of a plasticmaterial, comprising a capillary tube, a cylinder to receive thematerial to be tested, said cylinder connecting with the ends of saidcapillary tube, a reciprocable piston in said cylinder for alternatelypassing the material under observation in different directions throughsaid capillary tube, means to reciprocate said piston,fpressuredetermining means connecting with the ends of said capillary tube, meansfor,

determining the rate of flow through said capillary tube, and means formaintaining said capillary tube and the material under observation at asubstantially constant temperature.

2. A device for determining the flow characteristics of a plasticmaterial, comprising a capillary tube, a cylinder to receive thematerial to be tested, said cylinder connecting with the ends of saidcapillary tube, a reciprocable piston in said cylinder for alternatelypassing the material under observation'in different directions throughsaid capillary tube, means to reciprocate said pisasoacco ton, pressuredetermining means connecting with the ends of said capillary tube, meansfor timing the stroke of saidpiston, and means for maintaining saidcapillary tube and the material under observation at a substantiallyconstant temperature.

3. A device for determining the flow characteristics of a viscousmaterial, comprising a capillary tube, a cylinder to receive thematerial to be tested, said cylinder connecting with the ends of saidcapillary tube, a reciprocable piston in said cylinder for alternatelypassing the material under observation back and forth through saidcapillary tube, an engine to reciprocate said piston, pressuredetermining means connecting with the ends of said capillary tube, meansfor timing the-stroke of said piston to determine the rate of now ofmaterial through said capillary tube, and means .for maintaining saidcapillary tube and the material under observation at a substantiallyconstant temperature.

4. A device for determining the iiow characteristics of a viscousmaterial, comprising a capillary tube, a cylinder to receive thematerial to be tested, said cylinder connecting with the ends of saidcapillary tube, a reciprocable piston in said cylinder for alternatelypassing the material under observation back and forth through saidcapillary tube, an engine to reciprocate said piston, pressureresponsive means connecting with the ends of said capillary tube todetermine the pressure diilerential thereacross, vmeans for timing thestroke of said piston to determine the rate of ilow of material throughsaid capillary tube, and means for maintaining said capillary tube andthe material under observation at a subvbaci: and forth through saidcapillary tube, a reciprocating engine operatively connecting with saidpiston to provide motivation therefor, pressureresponsive meansconnecting with the ends of said capillary tube and exhibiting meansassociated therewith for determining the pressure differential acrosssaid capillary tube, means for timing the stroke of said piston todetermine the rate oi now oi material through said capillary tube, and aconstant temperature bath for maintaining said capillary tube and thematerial under observation at a substantially constant temperature.

6. A device im determining the iiow characteristics of a viscousmaterial, comprising a capillary tube. a cylinder to receive thematerial t0 be tested, means connecting the ends of said cylinder withthe ends of said capillary tube. a reciprocable piston in said cylinderior alternately passing the material under observation back and forththrough said capillary tube. a variable speed reciprocating hydraulicengine operatively connecting with said piston to provide motivationtherefor, pressure responsive means connecting with the ends of saidcapillary tube and exhibiting means associated therewith'l fordetermining the pressure diiierential across said capillary tube, a pairof electrical contacts operable by said reciprocating engine and timingmeans controlled by said contacts for timing the stroke of said pistonto determine the rate o! ow ofA material through said capillary tube,and a constant temperature bath for maintaining said capillary tube andthe material under observation at a substantially constant temperature.

7. In a grease viscometer characterized by a capillary tube and pressureresponsive means to determine the pressure diiierential thereacross asgrease is passed through said capillary tube, the improvement whichcomprises a cylinder to receive the grease to be tested, meansconnecting the ends of said cylinder with the ends of said capillarytube respectively, and a reciprocable piston in said cylinder toalternately force the grease under test back and forth through saidREFERENCES CITED The following references are of record in the le ofthis :patent:

FOREIGN PATENTS Country Date f Great Britain June 17, 1920 Number

